In accordance with recent trends for miniaturizing and making electric and electronic machinery and tools of high performance, materials for components, such as connectors to be used therein, have been required to be improved in every characteristic strictly.
Concretely, for example, the thickness of a sheet to be used at the contact point of a spring of a connector, has become so thin that it is difficult to ensure sufficient contact pressure. That is, in the contact point of a spring of a connector, generally, a contact pressure required for electrical connection is obtained from counterforce obtained by previously deflecting a sheet (a spring sheet). Therefore, a larger degree of deflecting is needed to obtain the same degree of contact pressure when the sheet is thinned. However, the sheet may undergo plastic deformation when the deflecting degree exceeds the elasticity limit of the sheet. Accordingly, additional improvements of the elasticity limit of the sheet have been required.
A variety of other characteristics, such as stress relaxation property, heat conductivity, bending property, heat resistance, plate adhesion property, and migration resistant property, have also been required for the material of the spring contact point of the connector. Mechanical strength, stress relaxation, heat and electric conductivity, and bending property are important, among the various characteristics.
While phosphor bronze has been frequently used for the spring contact point of the connector, it cannot completely satisfy the requirements described above. Accordingly, phosphor bronze is being replaced by a beryllium-copper alloy (an alloy prescribed in JIS C 1753) in recent years, which has higher mechanical strength and a good stress relaxation property, as well as good electric conductivity. However, the beryllium-copper alloy is very expensive, and metallic beryllium is toxic.
For these reasons, an inexpensive and highly safety material having the same level of characteristics as the beryllium-copper alloy has been urgently desired for use as the contact point material. Among various materials, a Cu—Ni—Si alloy relatively high in mechanical strength has been noted, and many investigations have been made since the latter half of the 1980s.
Unfortunately, the Cu—Ni—Si alloys developed during these years cannot serve as substitutes for the beryllium-copper alloy, considering copper alloys employed now. The reason is probably assumed to inferior mechanical strength and stress relaxation of the Cu—Ni—Si alloy compared with the beryllium-copper alloy.
Besides, a copper alloy in which stress relaxation of the Cu—Ni—Si alloy is improved, by adding Mg, has been proposed for use as the contact point material, but the same level of stress relaxation as the beryllium-copper alloy cannot be obtained by merely adding Mg, and innovative technologies are still required.